The present invention relates to copolymers of ethylene with propylene, optionally with a minor amount of polyenes, and to the process for their preparation.
Copolymers of ethylene with one or more xcex1-olefins and optionally a minor amount of polyenes are known which, after vulcanisation exhibit elastomeric type properties. The most common of these are copolymers of ethylene with propylene (EPR), which can contain small amounts of a non-conjugated diene monomer (EPDM).
Thanks to their good resistance to high temperatures, chemical and atmospheric agents, and their dielectric properties, these elastomers find uses in various application fields. Principally they can be used as additives for lubricating oils, covering materials in building, electric insulators, components in the automotive industry or modifiers in mixtures with thermoplastic polymers.
The above mentioned ethylene copolymers are generally prepared in the presence of Ziegler-Natta catalysts. The copolymers so obtained have a high tendency to produce blocks of propylenic units in the chain, and this gives rise to crystallinity negatively influencing the final characteristic of the product. Therefore, in order to obtain vulcanised copolymers which are endowed with good elastomeric properties, it is important that the distribution of the propylenic units within the chain is as homogenous as possible.
More recently, these ethylene copolymers have been prepared in the presence of homogeneous catalysts obtained from metallocenes and aluminoxane compounds.
U.S. Pat. No. 5,001,205, for example, describes a process for the preparation of elastomeric copolymers of ethylene with an xcex1-olefin, particularly with propylene, in which the product obtained from the reaction of methylaluminoxane (MAO) with a bis cyclopentadiene of Zr, Ti, or Hf, such as bis(tetrahydroindenyl)zirconium dichloride, ethylene-bis(tetrahydroindenyl)zirconium dichloride, or dimethylsilandiyl-bis(tetrahydroindenyl)zirconium dichloride is used as a catalyst.
The homogeneity of the distribution of the propylenic units in the copolymer that is obtained operating in the presence of these types of catalyst, although turning out improved with respect to the copolymers obtained from Ziegler-Natta catalysts, is still not totally satisfactory.
Hence, it would be extremely advantageous to obtain copolymers of ethylene with propylene, and optionally with minor amounts of polyenes, in which the homogeneity of the distribution of the propylenic units is sensibly improved.
It has been unexpectedly found that, by carrying out the polymerisation reaction in the presence of particular metallocene catalysts it is possible to prepare ethylene/propylene copolymers or ethylene/propylene/diene terpolymers in which the distribution of comonomers in the polymeric chain results extremely homogeneous.
It is therefore an object of the present invention a copolymer of ethylene with propylene, optionally with one or more polyenes, having a content of ethylene derived units comprised between about 35 and 85% by mole, a content of propylene derived units comprised between about 10 and 60% by mole and a content of polyene derived units comprised between about 0 to 5% by mole, having the following characteristics:
(A) the % by mole content of propylene in the copolymer (%P) and the ratio EPE/(EPE+PPE+PPP), wherein EPE, PPE and PPP represent the sequences ethylene/propylene/ethylene, propylene/propylene/ethylene and propylene/propylene/propylene respectively in the copolymer, satisfy the following relationship:
0.01%P+EPE/(EPE+PPE+PPP)xe2x89xa71
(B) less than 2% of the CH2 groups in the polymeric chain are in sequences (CH2)n, wherein n is an even number.
Another object of the present invention is an elastomeric copolymer obtainable by subjecting the above said copolymer to a vulcanisation process.
Still another object of the present invention is a shaped article obtained from an elastomeric copolymer according to the invention.
A further object of the present invention is a process for the preparation of the above said copolymers of ethylene.